The purpose of this proposal is to further investigate the structural proteins of polyoma virus and to determine their respective role(s) in the virion structure, virion assembly, viral infection and cell transformation. The unique aspects of our proposed investigation include: I. The structural proteins of the various temperature sensitive (ts) mutants will be studied by in vitro disassembly and reassembly of virions, to determine their biophysical characteristics, protein composition and which of the structural proteins are temperature sensitive. This study will utilize in vitro assembly experiments involving the dissociation products from wild type virions and ts mutants; in vivo isolated assembly intermediates and in vitro isolated capsomeres; and individually isolated DNA, histones and capsomere ingredients. II. The structural organization of polyoma virions will be studied to determine the virion location of the VP1 species, VP2 and VP3, domain of post-translational modifications (acetylation, methylation, sulfation) and the identification of inter and intramolecular disulfide linkages. III. To identify the cellular (cytoplasm or nucleus) location for post-translational modifications of polyoma polypeptides; and to determine what effect (i.e. regulatory) the isolated polypeptides and capsomeres might have on cellular and viral macromolecular synthesis and possible involvement in cell transformation. IV. The mechanism of in vivo polyoma assembly will be investigated to determine the optimum conditions for the isolation of the various assembly intermediates and to determine their biochemical, biophysical, protein composition and post-translational modifications during virion maturation. V. To further investigate the fate of the "input" infecting virions and their associated polypeptides during the early events of infections, and will include studies dealing with virion adsorption, identification and isolation of the cellular receptor, and the nucelar uncoating of polyoma virions.